UWB Antenna

1
UWB Antenna

• UWB antenna for indoor wireless applications
• Broadband
• Omni-directional
• Small size
• Small size ? Narrowband
• Antenna Q (?3)/(antenna size)
• Almost impossible to have 50ohm radiation
  resistance over the whole bandwidth
• Small size ? Omni-directional
• Phase difference on the antenna is small

6cm Dipole Antenna Input Impedance
Resistance
Reactance
Reactance Dominates!
2
Small Antenna Modeling
Take small Loop Antenna as an example

• E-fields in all directions are with almost the
  same waveform
• Only one resistor in our model
• By superposition, waveform across Rrad is equal
  to the far-zone E-fields
• Can estimate radiated E-field in SPICE

3
UWB Pulser/Antenna Co-design

• Large Current Radiator (LCR) as the UWB antenna
• Notch filter for FCC radiation mask

• H-bridge pulser to drive inductive load
• Flexible driving force by parallel structure

4
H-bridge Simulation Results

• Doublet is generated
• Pulse-width 1nS
• Smoothed after low-pass filtering at the receiver

• Meet FCCs rule
• EIRP will increase when PRF(Pulse Repetition
  Freq) increases

VRrad
FCC Mask
Vfiltered
EIRP (dBm/MHz)
Time(ns)
Frequency (GHz)
5
Sub-mW UWB LNA Design

• Specifications
• Fully-differential for on-chip interference
  immunity
• Voltage Gain gt 15dB
• 3dB BW 0.11GHz
• NF lt 6dB
• Linearity doesnt matter
• Input impedance 50ohm
• Goal Minimize power consumption (lt 1mW)
• Low input impedance sets the power consumption
• Whats the best LNA topology?

Z
LNA
LNA
6
Current-Reuse Technique
Shunt-Feedback
Common-Gate

• PMOS are added in as amplifying devices
• No extra DC current
• Gm gmn gmp
• Rin is halved
• Voltage gain is doubled
• NF decreased by 3dB
• BW decreased but OK

Rin 1/(gmngmp) Rin,diff 2/(gmngmp)
Rin 1/(gmngmp) Rin,diff 2/(gmngmp)
7
FB/CG Hybrid LNA

• Mp1/Mn1/Rf1act as FB Amp to Vin and CG Amp to
  Vin-
• Mp2/Mn2/Rf2 act as FB Amp to Vin- and CG Amp to
  Vin
• Rin 1/ 2(gmngmp)
• For Rin 50ohm,
• gmn gmp 5mA/V
• ? 8 times smaller than 40mA/V in CG or Shunt-FB
  amplifier!
• ? sub-mW LNA feasible
• Av 2(gmngmp)Rf

8
LNA Schematic Simulation
Av
NF
dB
s11
Frequency(MHz)

• Back-gate Cross-coupling enhances Gm by 10
• Coupling cap value 40pF

• Power 0.61mW
• All the specs are met

9
UWB LNA Layout w/o Capacitors
Mb1 Mb2

• ST Microelectronics 0.13um CMOS triple-well
  process
• Layout area
• 59um x 45um
• Common-centroid layout for good transistor
  matching
• Dummy for good resistor matching
• Capacitors not shown

Mp1
Mp2
Rf2
Mp1
Mp2
Rf1
59um
Mn2
Mn1
Mb3 Mb4
Mn2
Mn1
45um